A FEM/Kirchhoff-Helmholtz integral model for noise diffractors on low height noise barriers

So-called noise diffractors are a novel way to reduce traffic noise. As opposed to blocking or absorbing noise, diffractors bend noise in an upward direction, creating a shadow zone of reduced noise levels behind the diffractor. The diffraction is most effectively induced by quarter-wavelength resonators. These resonators can be placed in the ground but can also be mounted on top of a (low height) noise barrier. In this paper, we describe a finite element/Kirchhoff-Helmholtz integral model for a diffractor mounted on a low height noise barrier. The finite element model is used to calculate the scattered acoustic field in the proximity of the diffractor allowing for noise sources at larger distances from the diffractor. The acoustic pressure and particle velocity on the outer boundary of the finite element domain are subsequently used in the Kirchhoff-Helmholtz integral to evaluate acoustic pressures in the far field. The major benefit of this approach is a large reduction of the model size and calculation times. This allows us to efficiently assess the reduction for different barrier heights, larger source-to-diffractor distances and larger distances from diffractor to evaluation points.